This invention relates to the bombardment of surfaces by beams of ions.
Ion bombardment has been widely used in recent years as a method of implanting into a target and of sputtering a deposit of the material of the target onto a substrate. This is usually carried out under vacuum conditions and involves directing a stream of ions at the target. Collisions of the ions with atoms or molecules of the target during implantation impart enough energy to some of these atoms or molecules to free them from the body of the target. They are then directed or attracted to the substrate and deposited on the substrate.
The flow of ions involves not only a transport of mass but also the flow of an electric current. The path of current in an apparatus for sputtering thus involves a complete circuit that includes the source of the beam of ions, the beam itself, the target, and a return through a power supply to the source. Such systems work very successfully when the target is an electrical conductor which thus supplies an equipotential surface upon which the beam of ions impinges. However, several disadvantages become apparent if it is desired to direct such a beam at an insulating target, either for sputtering of atoms or molecules of the insulator onto another surface or to implant ions from the beam into the insulator. An attempt to direct an ion beam onto the surface of an insulator causes a local buildup of charges that repel the beam from the surface of the insulator. Such a beam can be seen to wander about on the surface, resulting in uneven areal implantation of ions and uneven removal of material for sputtering. The wandering occurs because areas that are locally charged repel the beam, causing it to be directed to areas that have accumulated less charge. Sometimes the buildup of charge is sufficiently great to deflect the beam entirely from the target until the charge has leaked away. This results in unsatisfactory operation, either for ion implantation or for sputtering.
It is an object of the present invention to provide a better method and means of sputtering insulating material from a target onto a substrate.
It is a further object of the present invention to provide a better method and means of implanting ions into an insulator.
Other objects will become apparent in the course of a detailed description of the invention.